Airfoils for 8020 40-4040 roof rack crossbars

Note: Please be sure to use the R1 STL models. They have better clearance hole sizes.

I have a roof rack on my camper van that is 69 inches wide. It has two 8020 40-4040 crossbars across the top. These 3D-printed shapes are intended to improve the aerodynamics of the crossbars to reduce drag and improve fuel economy.

The assembled wing profile is 1.57" (40mm) thick by 4.76" wide. The thickness-to-chord length ratio is 33%.

The length of each part, 8.6 inches, is limited by my printer. It takes 8 of each part to fill one 69-inch rail. I can print 4 of each part at a time. I have included STL files with other lengths for different applications.

Each part includes keys to align it along the T-slots in the rails, and one part to the next one, end to end. Sections may be removed and/or separated where gaps are needed.

Each part is fastened to the rails using one M6x20mm socket head cap screw, one M6x12mm washer, and one M6 slide-in hammerhead T-nut for 40-series T-slot rails. Stainless steel hardware is recommended.

I printed these with 0.2mm layers and 15% infill. I strengthened the area around the screw hole by adding a cylinder-shaped modifier the diameter of the washer (~12mm) with increased solid layers and perimeters of 6/4/6.

I installed the parts with blue thread-lock fluid and tightened the screws to just snug to avoid over-stressing the hole.

The parts were designed in Solidworks. The length of the parts is easy to modify as needed.

These should be made with PETG for rigidity and resistance to UV and high temperatures. ASA would also be a good material. The parts should be printed lengthwise with supports.